The present invention relates to a reference gamma compensation voltage generation circuit for an LCD source driver.
In a conventional LCD source driver, a reference gamma compensation voltage generated by an external circuit is supplied to driver chips. Of the source drivers that are presently in use, one employs a resistor array to reduce the number of inputs to the driver chips. However, due to resistance variations, reference voltage differences appear between the driver chips, and to compensate for this while employing the reference voltage, all the driver chips are mutually interconnected. Thus, the original object, the reduction in the number of driver chip inputs, is not achieved, and furthermore, since the gamma characteristic that is to be compensated for is fixed, a source driver must be specifically prepared for each LCD panel.
To resolve the above conventional shortcoming, it is one object of the present invention to provide a reference gamma compensation voltage generation circuit that, to generate a reference gamma compensation-voltage, employs an internal circuit to reduce the number of inputs to an LCD driver chip, and that, when multiple LCD driver chips are employed, can reduce the incidence of resistance variations among these chips.
According to a first aspect of the present invention, to achieve the above object a reference gamma compensation voltage generation circuit comprises: a counter, for system clocks, that generates a clock count value; a register, for storing a gamma compensation function value that is set, after the power is turned on; signal generation means, for employing the clock count value and the gamma compensation function value to generate a PWM signal wherein, for each gamma compensation cycle, the gamma compensation function value is represented as a pulse width; and a voltage generation circuit, for employing the PWM signal to generate a reference gamma compensation voltage.
It is preferable that the signal generation means compare the clock count value with the gamma compensation function value-to generate-the PWM signal.
It is also preferable that the voltage generation circuit filter the PWM signal to generate the gamma compensation function value.
In addition, according to a second aspect of the present invention, to achieve the above object a reference gamma compensation voltage generation circuit comprises: a counter, for generating a count value that represents a gamma compensation cycle; a register, for storing a gamma compensation function value that is set after the power is turned on; signal generation means, for employing the count value and the gamma compensation-function value to generate a PDM signal that represents the gamma compensation function value as the number of pulses for each gamma compensation cycle; and a voltage generation circuit, for employing the PDM signal to generate a reference gamma compensation voltage.
It is preferable that the voltage generation circuit filter the PDM signal to generate the gamma compensation function value.